The present invention relates to the field of one-way clutches for use in land motor vehicles and, more particularly, to a high performance sprag clutch assembly for use in the torque converter stator of an automatic transmission.
The original concept of the sprag clutch was developed in the late 1940s. Since that time sprag clutches have been used as driving members in many automatic transmissions worldwide. Sprag clutches are a specific class of one-way clutches. The unique feature of one-way clutches is that they can maintain high torque capacity in one direction and no torque capacity in the other direction.
The geometric design characterizing sprag clutch operation basically involves unidirectional wedging of the surfaces of multiple-cam structures denoted as dogleg sprags or sprag elements between two races, which enclose the sprags. The primary role of the sprag clutch in the present application is to allow the stator component within a torque converter in an automatic transmission to be driven by the torque converter in only one direction. This occurs at high load conditions during which the sprag elements are wedged in the drive mode to prevent relative motion between the inner and outer races. In this mode and during the transition to engagement, the wedged sprags transmit torque from the outer race to the inner race of the clutch.
Reliable sprag clutch operation requires a number of contributing design factors. (1) The clutch design must force all of the sprags to work together in phase throughout their operating range (so-called “phasing”) such that the sprags equally share the load within small tolerance variations. (2) All sprags should be individually energized, axially aligned, and as free as possible of parasitic friction that subtracts from the normal energizing forces. (3) Adequate race proportions, concentricity, material, heat treatment, and surface finish are essential. Thus, the clutch is no better than the races used in its fabrication. (4) The clutch must be adequately lubricated. Lubrication requirements will vary significantly depending on application details.
The typical problem in sprag clutch design is to achieve the greatest possible torque capacity in a minimum of space. Maximum and minimum sprag lengths are usually governed by practical considerations. For example, the maximum length is limited by the ability to heat-treat without distortion; and the minimum length is governed by the division of the axial space available between sprag and the energizing means (i.e. cages).
There are several known prior art patents that are available in the field and their discussion follows. One example of a prior art one-way clutch is disclosed in U.S. Pat. No. 5,779,014 to Kinoshita et al., which teaches a one-way clutch mounting structure including an outer ring, an inner ring and a plurality of clutch members interposed between the inner and outer rings. In this one-way clutch the outer ring is mounted in a housing, which is part of a stator. The housing has an annular section and a side section, which together define a pocket wherein the outer ring is mounted. The outer ring includes a spiral engaging means providing an integrated structure between the stator housing and the outer ring.
Another example of a prior art one-way clutch for a torque converter is disclosed in U.S. Pat. No. 5,760,514 to Taniguchi et al., which provides a one-way clutch for a plastic stator capable of preventing the inner circumferential surface of the outer ring of the one-way clutch from being deformed during shrinkage of the plastic stator in the manufacturing process. Thus, the outer ring integrally formed with the plastic stator is not required to be further machined after the integration, which reduces production costs.
U.S. Pat. No. 6,481,549 to Kroll et al. discloses an overrunning clutch for a torque converter wherein the stator consists of glass reinforced plastic which is injected around the overrunning clutch outer ring so that machining of the outer ring is no longer necessary after integration in the stator.
U.S. Pat. No. 5,881,556 to Matsuoka discloses a stator for a torque converter with thrust supporting structures without using a thrust bearing on at least one axial end thereby facilitating reduction of the axial dimensions thereof.
While these devices fulfill their respective, particular objectives and requirements, the aforementioned patents do not disclose the high performance sprag clutch assembly of the present invention, which substantially departs from the conventional concepts and designs of the prior art.